1. Field of the Invention
The present invention relates to a magnetic head structure.
2. Description of the Related Art
A magnetic disk apparatus includes a plurality of disks and a plurality of magnetic head structures arranged between the disks. The magnetic head structure is arranged in a magnetic head slider. The surface of the magnetic head slider facing the disk is called a floating surface. The magnetic head structure comprises a coil, a magnetic pole allowing a magnetic flux generated by the coil to be transmitted therethrough and forming a magnetic gap, an insulating layer surrounding the coil, and a protective layer covering the insulating layer and the magnetic pole, with these members being provided on a substrate forming the magnetic head slider. Also, a shield and a reading element (MR element) are arranged on the substrate.
When data are written into the disk, an electric current is supplied to the coil. The electric current flowing through the coil generates a magnetic flux, and the magnetic flux leaking in the magnetic pole writes data in the disk. Also, when data are read from the disk, data is read by the MR element. Recently, the flying height (amount of the floating) of the magnetic head slider has been reduced in order to increase the recording density, and the flying height is ten and several nm, for example.
In the magnetic head structure, the substrate is made of Al2O3—TiC, the coil is made of copper, the magnetic pole and the shield are made of a magnetic material such as NiFe, the protective layer is made of alumina, and the insulating layer is made of a resin material such as a photoresist. In this manner, the whole magnetic head structure is covered by a protective layer made of alumina, and the coil and the insulating layer, which have coefficients of thermal expansion different from that of the protective layer, are arranged within the magnetic head structure.
The coefficient of thermal expansion of alumina is 5.8×10−6, the coefficient of thermal expansion of copper is 17.2×10−6, the coefficient of thermal expansion of Permalloy as a magnetic material is 10×10−6, and the coefficient of thermal expansion of a photoresist is 30-70×10−6. The coefficient of thermal expansion of copper or a magnetic material is approximately two or three times greater than that of alumina. The coefficient of thermal expansion of photoresist is approximately 10 times greater than that of alumina.
When the temperature of the interior in the magnetic disk apparatus rises or when the temperature rises due to the supply of the electric current, thermal deformation may occur in the magnetic head structure due to the difference in coefficients of thermal expansion of the constituent materials of the magnetic head structure. Such thermal deformation may cause deformation of the floating surface.
In considering the deformation in the floating surface, the insulating layer comprising a photoresist and having the greatest coefficient of thermal expansion expands to the greatest degree, and therefore, such a phenomena occurs that a portion of the floating surface where the magnetic pole protrudes toward the disk. If the deformation in the floating surface occurs, the minimum amount of the floating of the magnetic head slider is substantially reduced, and it is possible that a portion of the floating surface near the magnetic pole contacts the disk, and the reliability may be reduced.
Therefore, it is desirable to reduce the protrusion of the portion of the floating surface near the magnetic pole toward the disk.
Conventionally, there is a proposal to reduce the protrusion of the portion of the floating surface near the magnetic pole toward the disk, by changing the materials of the insulating layer and the protective layer. For example, the protective layer is divided into two portions, in which a material having higher Young's modulus is used for the portion near the floating surface and a material having lower Young's modulus is used for the portion remote from the floating surface (refer to Japanese Unexamined Patent Publication (Kokai) No. 2000-306213, for example). Also, these is a proposal to use a resin having a lower glass transition temperature for the insulating layer (refer to Japanese Unexamined Patent Publication (Kokai) No. 2000-306215, for example). However, as there is a large difference between coefficient of thermal expansion of the protective layer and that of the insulating layer, as described above, the problems of the thermal deformation cannot be fundamentally solved even if a difference between coefficient of thermal expansion of the protective layer and that of the insulating layer is slightly reduced.